1. Field of the Invention
This invention relates to a process for upgrading hydrocarbons of relatively low boiling point and relatively poor antiknock properties into hydrocarbons having higher antiknock ratings and suitable for use as motor fuel blending stocks. More particularly, the invention relates to the use of a catalyst consisting essentially of trifluoromethanesulfonic acid for the conversion of natural gasoline derived from natural gas into a gasoline product of higher octane number than the original charge stock.
2. Description of the Prior Art
Saturated highly branched-chain paraffin hydrocarbons, and particularly mixtures thereof, occurring in gasoline fractions are very desirable motor fuel components because of their antiknock properties. It is known, for example, that the more highly branched chain isomers of paraffins are more valuable than the corresponding unbranched or less branched paraffins because of their higher octane rating. The 2,2-dimethylbutane isomer of hexane, for example, has an octane number of 92 whereas normal hexane has an octane rating of 25. Similarly, 2,2,3-trimethylbutane (triptane) also has a highly branched chain structure and provides fuel characteristics far exceeding the isoheptanes such as methylhexanes and dimethylpentanes. Because of its highly branched structure, the octane rating of triptane exceeds that of isooctane which has a rating of 100. The demand for motor fuelds of high octane value without lead additives has increased steadily and a variety of hydrocarbon processes have been suggested whereby various dydrocarbon oils, such as straight run gasolines, naphthas and similar hydrocarbon mixtures, have been upgraded to produce gasoline of higher octane value.
U.S. Pat. No. 3,594,445 discloses the isomerization of normal and naphthenic paraffins by employing a catalyst containing (1) a fluoride of a metal of Group V such as antimony pentafluoride and (2) a fluorosulfonic acid in the presence of hydrogen and an olefin and/or an alkyl fluorosulfonate.
U.S. Pat. No. 3,766,286 discloses the isomerization of paraffinic and/or alkyl substituted aromatic hydrocarbons with a catalyst comprising (a) a Lewis acid of the formula MX.sub.n where M is selected from Group IV-B, V or VI-B of the Periodic Table, X is a halogen and n varies from 3 to 6, and (b) a strong Bronsted acid comprising fluorosulfuric acid, trifluoromethanesulfonic acid, trifluoracetic acid or mixtures thereof.
U.S. Pat. No. 3,778,489 discloses the alkylation of a paraffin with separate olefin streams using a strong acid such as sulfuric acid, hydrogen fluoride, halosulfuric acid, trihalomethanesulfonic acid and the like.
U.S. Pat. No. 3,839,489 discloses the isomerization of paraffinic feedstocks using a catalyst consisting of arsenic pentafluoride, antimony pentafluoride, and mixtures thereof with either trifluoromethanesulfonic acid or hydrogen in the presence of hydrogen.
U.S. Pat. No. 3,996,116 discloses the conversion of straight-chain saturated hydrocarbons into branched-chain saturated hydrocarbons by ocidizing the hydrocarbons in liquid phase in the presence of a superacid such as HFSO.sub.3 by electrolysis at a voltage between the half wave voltage of the hydrocarbon and that of the superacid.
U.S. Pat. No. 3,852,184 relates to the isomerization of alkylcydopentane in a reforming feed to cydohexanes in the presence of hydrogen employing a catalyst mixture of a metal halide and a protonic acid, preferrably hydrogen halide. As other alternate, protonic acids fluorosulfonic acid, monofluorophosphoric acid, difluorophosphoric acid, trifluoromethanesulfonic acid, trifluoroacetic acid and bis(perfluoromethylsulfonyl)methane are suggested.
U.S. Pat. No. 4,035,286 discloses the octane upgrading of light naphtha streams using as catalyst a mixture of antimony pentafluoride and a fluoroalkanesulfonic acid.
U.S. Pat. No. 4,044,069 discloses a process for the isomerization and alkylation of paraffinic hydrocarbons by means of a catalyst composition comprising a mixture of Lewis acids such as arsenic pentafluoride and a sulphonic acid corresponding to the general formula RF(SO.sub.3 H)p where RF represents an alkylperfluorinated or cycloalkylperfluorinated hydrocarbon radical having a number of carbon atoms between 2 and 8 and p is 1 or 2.
Other pertinent literature art includes the articles "Mechanism of Acid-Catalyzed Isomerization of the Hexanes" by D. A. McCaulay (Std. Oil Co. 1959) J. Am. Chem. Soc., Vol. 81, p. 6437, "Trifluoromethanesulfonic Acid and Derivatives" by R. D. Howells and J. D. McCown, Chemical Reviews, Vol. 77, No. 1, p. 69, and "Superacids", by George A. Olah et al., Science, Vol. 206, p. 13.